Moreno Fernández, Harol ; Alkemper, Achim ; Wang, Kai ; Mempin, Crizaldo Jr. ; Gallenberger, Julia ; Hofmann, Jan P. (2024)
Kinetic analysis of the self-discharge of the NiOOH OER active phase in KOH electrolyte: insights from in-situ Raman and UV-Vis reflectance spectroscopies.
In: Journal of Catalysis, 440
doi: 10.1016/j.jcat.2024.115823
Artikel, Bibliographie

Kurzbeschreibung (Abstract)

NiOOH has been established as the active phase of NiO-based electrocatalysts in the alkaline Oxygen Evolution Reaction (OER). Here, we investigate the self-discharge behavior of NiOOH electrodes under open circuit potential (OCP) conditions in 1 M KOH electrolyte by monitoring phase changes via in-situ Raman and UV-Vis reflectance spectroscopies and performing kinetic analyses on the OCP and spectroscopic data. Our findings reveal a linear phase change from NiOOH to Ni(OH)2 over time, indicative of a 0th-order reduction reaction. Contrarily, the OCP evolution associated with this phase reduction displayed a combination of linear and exponential decay patterns as a result of various kinetics, including Faradaic processes and diffusion-controlled mechanisms, influencing the self-discharge potential over 1.25Â V (vs RHE). An additional linear region at lower potentials (<1.25Â V (vs RHE)) suggests that charge redistribution due to the phase change from alpha-Ni(OH)2 to beta-Ni(OH)2 dominates the self-discharge, a behavior confirmed by in-situ UV-vis reflectance spectroscopy. These findings highlight the effectiveness of combining in-situ Raman and UV-Vis spectroscopy with electrochemical data for real-time monitoring of electrochemical processes, here potential-dependent electrocatalyst phase changes, leading to a more detailed and accurate understanding of the dynamic behavior, phase change kinetics, and self-discharge behaviors of solid electrocatalysts that can guide the design of more efficient and durable energy storage and conversion materials.

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